Problem 105 - A Complete Resource Book in Chemistry for JEE Main

Question

The reaction potential values of \(\mathrm{M}, \mathrm{N}\) and \(\mathrm{O}\) are \(+2.46,-1.13\) and \(-3.13 \mathrm{~V}\) respectively. Which of the following order is correct, regarding their reducing property? (a) \(\mathrm{O}>\mathrm{N}>\mathrm{M}\) (b) \(\mathrm{O}>\mathrm{M}>\mathrm{N}\) (c) \(\mathrm{M}>\mathrm{N}>\mathrm{O}\) (d) \(\mathrm{M}>\mathrm{O}>\mathrm{N}\)

Step-by-Step Solution

Answer

The correct order is (a) \( \mathrm{O} > \mathrm{N} > \mathrm{M} \).

Step 1: Understanding Reaction Potentials

Reaction potential, also known as standard electrode potential, is a measure of the tendency of a compound to gain electrons and thereby be reduced. A higher reaction potential indicates a stronger tendency to be reduced.

Step 2: Analyzing Given Reaction Potentials

The given reaction potentials are: M = +2.46 V, N = -1.13 V, and O = -3.13 V. To compare reducing properties, the element with the most negative reaction potential is the strongest reducing agent.

Step 3: Ordering Based on Reducing Properties

Since reducing agents are stronger when their standard electrode potential is more negative, we order the potentials from more negative to less negative: 1. O (-3.13 V) 2. N (-1.13 V) 3. M (+2.46 V). This means O is the strongest reducing agent and M is the weakest.

Step 4: Selecting the Correct Order

Considering the reducing properties deduced in Step 3, the correct order for strongest to weakest reducing agent is: O > N > M. Therefore, option (a) is the correct choice.

Key Concepts

Standard Electrode Potential

The standard electrode potential is a fundamental concept in electrochemistry. It is often denoted by the symbol \( E^0 \) and represents the measure of the tendency of a chemical species to be reduced, or gain electrons, under standard conditions. These standard conditions usually include a temperature of 298 K, a pressure of 1 atm, and solute concentrations of 1 M. Electrode potentials are measured in volts (V).
Understanding the standard electrode potential is crucial, as it helps predict the direction of redox reactions. The higher the standard electrode potential, the greater the species' ability to accept electrons and be reduced. Conversely, a lower or more negative value indicates a stronger tendency to give up electrons and thus act as a reducing agent. This concept plays a key role in determining the cell potential of electrochemical cells and is fundamental to understanding battery operations and corrosion processes.

Reducing Agent

A reducing agent, also called a reductant, is a substance that donates electrons to another species. During this electron transfer, the reducing agent itself becomes oxidized. In simple terms, a reducing agent reduces another substance and gets oxidized in the process.
Identifying reducing agents is crucial in analyzing redox reactions. Substances with more negative standard electrode potentials are stronger reducing agents because they are more willing to donate electrons. For example, in the given exercise, substance O with a reaction potential of \(-3.13 \text{ V}\) acts as the strongest reducing agent among M, N, and O. This indicates that O is more effective in donating electrons compared to the others, facilitating their reduction.

Reaction Potential

Although often used interchangeably with standard electrode potential, reaction potential refers to the measure of an electrochemical cell's voltage under specific conditions. It determines the cell's ability to drive an oxidation-reduction reaction.
Reaction potential is vital in assessing the feasibility of redox reactions in a cell. A positive reaction potential signifies that the reaction will proceed spontaneously, while a negative one indicates non-spontaneity under the given conditions. In electrochemical contexts, a reaction with a higher potential is favored in terms of reduction, which is why understanding and comparing reaction potentials, like in the exercise, helps in predicting the behavior of the substances involved.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, or redox reactions, are processes where electrons are transferred between two substances. These reactions involve oxidation, where a substance loses electrons, and reduction, where a substance gains electrons. In any redox reaction, one species is oxidized and another is reduced.
In electrochemistry, redox reactions are the basis of energy conversion in batteries and fuel cells. They are crucial for various industrial processes, including metal extraction and manufacturing.

• Oxidation - Involves loss of electrons and an increase in oxidation state.
• Reduction - Involves gain of electrons and a decrease in oxidation state.

The exercise showcases how redox reactions can be analyzed based on reaction potentials to predict the strongest reducing agent. Understanding these fundamentals helps predict how substances will behave in electrochemical systems, guiding us in designing efficient energy solutions and chemical processes.